If you have never been to Alaska there are many things to do in the main ports. We often do the b2b out of Vancouver and usually you hit Glacier Bay and Hubbard on one direction and Glacier Bay and College Fjord in the other.
I have never seen reservations available for Salty Dog Gastropub. It may vary ship to ship but on both the Crown and the Ruby (3 cruises in the las 7 months) there were no reservations only walk up. It is not my favorite casual venue.
Being so far forward and high up I would expect movement for anything but a standard Caribbean type cruise Any cruise involving the Pacific or Atlantic is going have more movement
We always book on board and have veneer had an issue getting into specialty dining with booking times between 7:30 and 8:00. They never book 100% prior to sailing